Towards bone-like elastic modulus in Ti[sbnd]Nb[sbnd]Sn alloys with large recovery strain for biomedical applications

Abstract

For biomedical titanium alloys, the reduction of their elastic modulus approximating that of human bone (~30 GPa) is highly required for using them as bone implant materials to reduce the risk of stress shielding. In this study, Ti-15Nb-(4-6)Sn (at%) shape memory alloys were developed to achieve the bone-like elastic modulus for biomedical applications by varying Sn content to adjust the factors such as transformation temperature, β stability, ω phase amount and texture component which are well known to affect the elastic modulus of titanium alloys. The elastic modulus of 68.8 GPa in the 4Sn specimen decreased to 41.5 GPa in the 5Sn specimen due to the suppression of α" martensite, achieving the least β stability and the decrease in the amount of athermal ω (ωath) phase. A good combination of low elastic modulus and room temperature superelasticity was obtained in the 5Sn specimen. Significantly, a bone-like elastic modulus of 31.5 GPa is achieved in the 5.5Sn specimen, which has not been reported yet in titanium alloy sheets. In this specimen, 110β001β (Goss texture) was developed as the dominant texture component and the ωath phase was completely suppressed. Also, the formation of the dominant Goss texture has not been reported previously in Ti–Nb–Sn alloy sheets. More detailly, along the rolling direction (RD), the [001]β//RD texture which effectively reduces elastic modulus along the RD was formed in 5Sn and 5.5Sn specimens and its intensity increased largely in the 5.5Sn specimen. Such a bone-like elastic modulus is attributed to the formation of a strong [001]β//RD texture as well as the absence of the ωath phase in β matrix.